Optical devices play a role in converting an electrical signal into light. Typically represented by an optical device, a light emitting diode (LED) has high efficiency and may produce light at high luminance, and the use thereof is thus drastically increasing.
However, because LEDs generate heat in the course of emitting light, they may deteriorate or may negatively affect performance of other parts.
Hence, thorough research is ongoing to manufacture substrates having high mechanical strength while efficiently dissipating heat generated from LEDs, but results thereof are unsatisfactory.
For example, republished Japanese Patent No. WO2006/070457 discloses a highly heat conductive circuit module. As illustrated in (A) to (F) of FIG. 1, metal layers 10 and insulating resin layers 20 are alternately stacked and then cured, and the resulting laminate L is cut, thus obtaining a package 30 in which the metal layers 10 and the insulating resin layers 20 are alternately shown on the cut surface. Then, electronic parts 40 are disposed on the package 30, after which the package 30 is longitudinally and transversely cut and divided into individual package pieces 32, thereby obtaining a plurality of circuit modules M having the metal layers and the insulating layers which are repeated, that is, an optical device substrate.
In such a conventional technique, the laminate including the metal layers 10 and the insulating resin layers 20 which are alternately stacked may be formed by applying a resin paste on the metal layers 10 and then stacking the metal layers, or by alternately stacking the metal layers 10 and the resin films 20, and to obtain adhesion between the metal layers 10 and the insulating resin layers 20, the surfaces of the metal layers 10 may be formed with an oxide film and roughened.
However, in the case where an optical device substrate is manufactured by oxidizing the surfaces of the metal layers 10 and then alternately stacking the metal layers 10 and the resin films 20, pores are present in the oxide layer formed on the metal layer 10 and thus the flat area of the oxide layer in contact with the resin film 20 becomes small, and thereby the metal layer 10 and the insulating resin layer 20 may be undesirably easily separated from each other even by a small force.
Also, in the case where an optical device substrate is manufactured by oxidizing the surfaces of the metal layers 10, coating the metal layers 10 with only a resin paste, namely, a liquid resin binder and then stacking the metal layers, the resin paste may bubble in the course of thermal curing of the resin paste, and thus mechanical strength of the insulating resin layer 20 may become very weak, undesirably easily breaking the optical device substrate.
Also, in the case where an optical device substrate is manufactured by oxidizing the surfaces of the metal layers 10, applying only a liquid resin binder and then stacking the metal layers, when the liquid resin binder is cured, its ductility disappears and is easy to break, and thus the insulating resin layer 20 of the optical device substrate may be undesirably easily broken.
Also, in the case where an optical device substrate is manufactured by oxidizing the surfaces of the metal layers 10, applying only a liquid resin binder and then stacking the metal layers, when the metal layers 10 stacked in a direction of gravity and then pressed using a press are thermally cured, a pressure applied to the lowermost layer and the uppermost layer may vary due to the weight of the metal layers 10, and thus the thickness of the insulating layers of the optical device substrate becomes very non-uniform.
Also, in the case where an optical device substrate is manufactured by oxidizing the surfaces of the metal layers 10, applying only a liquid resin binder and then stacking the metal layers, when the viscosity of the liquid resin binder is high, the liquid resin binder does not infiltrate the oxide films formed on the metal layers 10, whereas when the viscosity thereof is low, the liquid resin binder escapes between the metal layers 10 as soon as the layers are pressed, and undesirably the optical device substrate wherein the insulating layers are only partially provided may be produced.
Also, in the case where an optical device substrate is manufactured by oxidizing the surfaces of the metal layers 10, applying only a liquid resin binder and then stacking the metal layers, the liquid resin may flow down and thus it is very difficult to form the insulating layers at a predetermined thickness or more.
When only the liquid resin binder is used in this way, the thickness of the insulating layers of the optical device substrate is very difficult to uniformly maintain, thus making it considerably difficult to implement packaging of LED chips located at a predetermined interval on the optical device substrate by an automation system.
In addition, Japanese Patent Application Publication No. Hei. 9-55535 simply discloses fabrication of an optical device substrate by alternately stacking conductive members and epoxy adhesive layers and performing cutting in the same direction as the stacking direction, or by applying a liquid epoxy resin on conductive members, stacking metal layers and performing cutting in the same direction as the stacking direction. Thus, this patent also causes substantially the same problems as in republished Japanese Patent No. WO2006/070457 as above.